Theoretical Design of Core-Shell 3d-Metal Nanoclusters for Efficient Hydrogen-Evolving Reaction

Co- and Ni-based materials are promising catalysts for the hydrogen evolution reaction (HER) but usually transform into active Co/Ni metal nanoclusters during reductive HER processes, making the rational design of initial states for Co/Ni metal nanoclusters critical. However, the optimal states of Co/Ni metal nanoclusters for the HER are still unclear. Herein, we design 16 pure/alloyed core-shell Co/Ni-metal nanoclusters and give systematic insights into their HER performance and catalysis mechanism, from thermodynamics to kinetics. We find that the HER performance significantly depends on the geometric structures of the Co-Ni metal nanoclusters. Compared to other sized nanoclusters, Co₁₃@Ni₂₀ and Ni@Co₁₂@Ni₂₀ exhibit the optimum HER performance with proton adsorption free energies close to zero, which could be attributed to their special and favorable negative surface electronic structures to adsorb the key protons. Further investigations show that they also exhibit good stability in both thermodynamics and kinetics. Furthermore, we apply metadynamics to directly map the 2D free energy reaction surface and HER pathways, ultimately uncovering the detailed HER mechanism of the best-performing Co₁₃@Ni₂₀ catalyst. Our work helps us understand the optimal states and the catalytic mechanism of active Co/Ni metal nanoclusters for HER.